1. Field of the Invention
The present invention relates to a thermal transfer color printer which selectively transfers color-record forming materials (color materials) from a thermal ink ribbon, which has a plurality of color materials divided in the feed direction, to a record medium by applying thermal energy to localized areas on the thermal ink ribbon according to print data differentiated by the color material or identified with different colors and, more particularly, to a thermal transfer color printer which can reduce to a minimum the amount of thermal ink ribbon used.
2. Description of the Prior Art
Generally, a thermal transfer color printer is provided with a thermal head on a carriage which moves relative to a record medium, such as a print paper, and a thermal ink ribbon on which are spread a plurality of heat fusible color materials divided in the feed direction of the ink ribbon (the long direction). In order to cause the selective heat transfer of the color material onto the printing paper according to print data differentiated by the color material, the carriage is caused to move, while at the same time, the thermal ribbon is fed forward. A color sensor for detecting the position of the color material on the thermal ink ribbon is provided on the carriage. The feeding action of the thermal ink ribbon is carried out such that a leading section of the color material scheduled for printing is positioned on the thermal head, according to the positional data of the color material detected by the color sensor. There are two positioning methods commonly used for the color sensor of a conventional color printer. In one of these methods the color sensor is positioned at the ink ribbon upstream side of the thermal head. Then, after the detection of the tip of the color material scheduled to be printed by the color sensor, the tip position of each color material is moved from the sensor section to the thermal head with the rotation of an ink ribbon reel. However, in this method, the length of the ink ribbon wound by one rotation of the reel is determined by the diameter of the roll of ink ribbon on the winding side. This diameter gradually becomes larger the more the ink ribbon is used, so that there is usually a variation of two to three times from the time when the use of a new ribbon is started until the ribbon is almost finished. Accordingly, the length of the ink ribbon which is wound up also varies to the same extent. From the fact that this variation takes place, it is necessary to move the ink ribbon an extra distance so as to always come the tip position of each color material to the thermal head position, thereby wasting the amount of ribbon equivalent to this extra distance. In addition, in other printers the color sensor is positioned directly behind the thermal head, but in this case also, in the same way as the example of a conventional unit which has just been explained, an amount of the thermal ink ribbon relative to the distance between the color sensor and the thermal head is wasted.
In the thermal transfer method, the ink ribbon is heated by the thermal head and the ink is physically transferred from the localized areas on the ink ribbon, so that the ribbon cannot be reused. Accordingly, the ink ribbon is discarded after only one use, so that the cost of ink ribbons is high. In the thermal transfer method, therefore, the efficiency of the use of the thermal ink ribbon is extremely important in the finished product.
Also, in the thermal transfer color printer a slightly longer length of color material than one line of print length on the printing paper is separately coated in a plurality of successive colors, so that, even for a small amount of printing, more than one line of print length of ink ribbon uses in several parts of color. Therefore, the utilization efficiency of the ink ribbon is remarkably worsened, and the increase in running costs becomes a major problem.
In prior art thermal transfer color printers, the width of each color material section on the thermal ink ribbon is standard print width with a slight excess added. That is, it is set at the dimension of the standard width dimension of the print paper. As a result, one line of print is obtained by one color material portion. However, in actual practice, printed lines in which the printing carried out in one part only are the most prevalant, and this is particularly evident in color print. When such a print line is printed with the abovementioned prior art thermal transfer color printer, in spite of a large unprinted section being present on each printed line, in each print of line the amount of thermal ink ribbon relative to the standard print width is used. As a result, the thermal ink ribbon is not used effectively. Because of this, with the conventional configuration, there is the drawback that the amount of thermal ink ribbon used increases excessively, and this kind of drawback becomes even more evident, when multicolored portions are present on each printed line.
In prior art color printers, for each completion of one line of print action based on one line of print data, the initial search of the beginning of the color materials is carried out, in other words, the forefront of the prescribed color material is positioned in the heat generating portion of the thermal head. However, in the case where, when the power is cut, the user touches the thermal ink ribbon or its bobbin, and the position of that thermal ink ribbon deviates from the initial position. Therefore, when the print action is started in that position deviation status, there is the worry that a print mistake, print color error, or status where control is impossible, will be brought about. For this reason, conventionally, each time the power is applied, beginning-portion search is carried out.
Here, in the case where the color materials of the thermal ink ribbon are arranged in the order--yellow, magenta, cyan, for example, the print of a magenta color material only occurs on certain print lines, and on the next print line, for example, a cyan color material only is printed. When this happens, at the point in time when the printing of the magenta color material is completed, even though it is possible to print the cyan which follows, after the completion of the printing action of the magenta color material, the unused color materials in one color portion of yellow, magenta, and cyan is fed by the execution of the beginning-portion search. Therefore, there is the drawback which that part of the thermal ink ribbon is wasted, and because of this the problem of high running costs is incurred. In addition, when there is a deviation in the position of the thermal ink ribbon, and also in the case where the beginning-portion is searched when the power is applied, the spread portion of the unused color material is fed in the three colors of yellow, magenta, and cyan. This causes the waste of the thermal ink ribbon. In addition to this, because at the time of beginning-portion search, a thermal ink ribbon of three color parts or one line part must be fed, a comparatively long time is used for that feed action, and there is the problem that the print speed of the whole system becomes slow.
Furthermore, in prior art thermal ink ribbons, at the boundary section of the color materials, the adjacent color materials may be piled up and spread over, and the color sensor misdetects the color materials in that boundary section, and there is the drawback that the reliability of the position detection of the ink ribbon is reduced.
In prior art color printers, the use of a color cassette in which a thermal ink ribbon having a plurality of color materials is stored is usually used, and in the case where printing is done with a single color, a program in a host computer which controls the printer is necessary for use with a single color. Accordingly, when a single color cassette case, in which a thermal ink ribbon for single color is stored, is installed, there is the worry that, because the printer itself cannot distinguish a discrepancy in the color cassette, a print error could be produced, and printing is carried out as color printing.
Also, in order to prevent this from happening, it is necessary to go to the trouble of fully revising the program of the host computer.